One critical stage in the development of new electronic devices, such as those used in-flight by aircraft and spacecraft, is verification of the new device. For design verification, a prototype printed wiring assembly (PWA) should be as close as possible, if not identical, to the production PWA. However, during testing, a prototype PWA must also provide sufficient access to signals in order to verify the proper operation and debug of the electronic devices, such as discrete and integrated circuit (IC) devices, mounted on a printed wiring board (PWB) that is part of the PWA. This access is difficult to obtain where surface mount technology (SMT) area array devices (AADs), such as land grid array (LGA), ball grid array (BGA) or column grid array (CGA) devices or SMT socket-mounted pin grid array (PGA) devices populate the PWB because a significant portion of the input/output (I/O) connections at the interfacial AAD-PWB interface is not exposed and thus are inaccessible to probing. For many applications, such as military and space application, engineers attempt to maximize the density of components mounted on a PWB in order to reduce the volume and weight of the device. For this reason, a PWA may also have SMT devices mounted on both sides of a printed wiring board (PWB), further preventing access to AAD-PWB interface signals from the backside of the PWB.
Typically, testing AAD I/O signals requires placement and routing of additional test points and/or test connectors on the prototype PWA in order to bring out all the signals of the interfacial AAD-PWB interface. This leads to the disadvantage of designing one PWA for use in development testing that is different from a second PWA used for actual production and the addition of test points and/or connectors defeats the space saving advantages of AADs. Besides the extra costs and schedule resources required to produce two PWAs, the use of different PWAs increases the prototype PWA complexity and adds a significant amount of additional trace loading in the prototype PWA that is not present in the production PWA. These disadvantages ultimately make the prototype testing less valid for production design verification (e.g. because of prototype and production PWA timing differences). Boundary scans can provide an indirect indication of the signals at an interfacial interface, but are not useful for troubleshooting signal integrity or timing problems. Finally, conventional AAD test adapters in the art today are much larger than the AADs that they monitor. Thus they require a much larger attach pattern or footprint on the PWA than what the direct-mounted AADs would occupy, and they can overshadow any neighboring devices on the PWA, making the neighboring devices inaccessible for probing.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved methods and systems for testing prototype PWA populated with SMT AADs devices and other SMT electronic devices.